JP2004103546A - Positive active material composite particle, electrode using the same, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode active material-containing composition used in a lithium secondary battery combining output with cycle life under low temperature atmosphere in a high level, and to provide an electrode and the lithium secondary battery using the composition. <P>SOLUTION: A compression shearing stress is applied to a mixture of (A) a lithium-nickel compound oxide, (B) activated carbon, and (C) carbon black to manufacture positive active material composite particles. <P>COPYRIGHT: (C)2004,JPO

Description

【００５５】
また、表２に示す組成で上記で得られた複合化粒子、（Ｄ）及び（Ｅ）を用いて、リチウム二次電池正極活物質複合化粒子含有組成物を製造した。
なお、比較例１は、（Ａ）及び（Ｃ）の混合物に圧縮剪断応力を加える処理を施して得られたリチウム二次電池正極活物質複合化粒子に、（Ｂ）、（Ｄ）及び（Ｅ）を加えて製造したリチウム二次電池正極活物質複合化粒子含有組成物を用いた。
【００５６】
【表２】

【００５７】
各リチウム二次電池正極活物質複合化粒子含有組成物をＮ−メチル−２ピロリドンに分散して得られたスラリーを、厚さ２０μｍのアルミ箔の片面に塗布し乾燥させた後、直径１２ｍｍ（１２φ）の円形に打ち抜き、これをプレスして正極とした。正極中の活物質量は約１３ｍｇであった。
この正極塗布膜を９φに打ち抜いたものを試験極とし、Ｌｉ金属を対極としてコインセルを組み、これに０．２ｍＡ／ｃｍ^２の定電流で上限４．２Ｖ下限３．２Ｖで充放電する試験を実施し、正極活物質単位重量当たりの初期充電容量〔Ｑｓ（ｍＡｈ／ｇ）〕、初期放電容量〔Ｑｄ１（ｍＡｈ／ｇ）〕を測定した。
【００５８】
また、平均粒子径８〜１２μｍの黒鉛粉末９２．５重量部とポリビニリデンフルオライド「ＰＶＤＦ＃１３００」（呉羽化学工業製）７．５重量部とを、Ｎ−メチルピロリドンに分散させて調製したスラリーを厚さ２０μｍの銅箔の片面に塗布し、乾燥させた後、直径１２ｍｍの円形に打ち抜き、プレスして負極とした。
【００５９】
この負極を試験極とし、リチウム金属を対極としてコインセルを組み、これに０．２ｍＡ／ｃｍ^２の定電流で負極にリチウムイオンを吸蔵させる反応を下限０Ｖで行ったときの、負極活物質単位重量当たりの初期吸蔵容量〔Ｑｆ（ｍＡｈ／ｇ）〕を測定した。
正極缶の上に正極を載置し、その上にセパレータとして厚さ２５μｍの多孔性ポリエチレンフィルムを載置し、ポリプロピレン製ガスケットで押さえ、その上に負極を載置し、更に厚み調整用のスペーサーを載置した。これに、エチレンカーボネートとエチルメチルカーボネートの混合溶媒（容積比３：７）に六弗化燐酸リチウム（ＬｉＰＦ_６）を１モル／リットルとなるように溶解させた電解液を加えて十分に滲み込ませた後、負極缶を載置し、封口することによりコインセルを作製した。なお、正極活物質重量／負極活物質重量＝｛〔Ｑｆ（ｍＡｈ／ｇ）〕／１．２｝／〔Ｑｃ（ｍＡｈ／ｇ）〕となるように設定した。
【００６０】
コインセルについて、コンディショニング電流値〔Ｉ（ｍＡ）〕＝〔Ｑｄ１（ｍＡｈ／ｇ）〕×正極活物質重量／５で、充電上限電圧４．１Ｖ、放電下限電圧３．０Ｖとして、充放電２サイクルの初期コンディショニングを行い、２サイクル目における正極活物質単位重量当たりの放電容量〔Ｑｄ２（ｍＡｈ／ｇ）〕を測定した。
【００６１】
電池を十分緩和した後、１時間率電流値〔１Ｃ（ｍＡ）〕＝〔Ｑｄ２（ｍＡｈ／ｇ）×正極活物質重量として、定電流１／（３Ｃ）で７２分間充電を行い、１時間静置した。次いで、−３０℃の低温雰囲気下で１時間以上静置した後、定電流２．５Ｃで４秒間放電を行った。このときの放電直前のＯＣＶ（Ｏｐｅｎ　Ｃｉｒｃｕｉｔ　Ｖｏｌｔａｇｅ）と放電４秒後のＯＣＶとの差（ΔＶ）を測定することにより、クロノポテンショメトリーを測定した。結果を表２に示した。ΔＶが小さい程、電池の抵抗が小さく大電力の取り出しが可能であり、低温雰囲気下での出力が向上していることを意味する。
【００６２】
また、初期コンディショニング後のコインセルを、６０℃雰囲気下で、定電流１Ｃ、充電上限電圧４．１Ｖ、放電下限電圧３．０Ｖとして、充放電を１００サイクル繰り返した。引き続き０．２ｍＡの充放電を２回繰り返し、サイクル後の容量を確認した。サイクル後２回目の放電容量をサイクル後のＱｄ２としてクロノポテンショメトリーの測定を実施した。結果を表３に示した。
【００６３】
【表３】

【００６４】
【発明の効果】
本発明に係るリチウム二次電池正極活物質複合化粒子を含有する組成物を用いることにより、低温雰囲気下での出力及びサイクル寿命に優れたリチウム二次電池を作製することができる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to composite particles of a positive electrode active material used in a lithium secondary battery, and an electrode and a lithium secondary battery using the composite particles.
[0002]
[Prior art]
Lithium secondary batteries are excellent in energy density and output density, and can be reduced in size and weight. Therefore, lithium secondary batteries have shown rapid growth as power supplies for portable devices such as notebook computers, mobile phones, and handy video cameras. In addition, it has attracted attention as a power source for electric vehicles and load leveling of electric power.
[0003]
A positive electrode used in a lithium secondary battery is generally composed of a current collector and a positive electrode active material layer formed on the surface thereof and containing a positive electrode active material, a conductive agent and a binder. As the positive electrode active material, a composite oxide of lithium and a transition metal such as manganese, cobalt or nickel, such as a lithium-manganese composite oxide, a lithium-cobalt composite oxide, or a lithium-nickel composite oxide, has high performance battery characteristics. Is gaining attention. A lithium secondary battery using these lithium-based composite oxides has an advantage that a high voltage can be obtained and a high output can be obtained. Currently, studies are actively being conducted to improve the stability of composite oxides, increase the capacity of batteries, and improve battery characteristics at high temperatures.
[0004]
Japanese Patent Application Laid-Open No. H11-154515 discloses a lithium-based composite oxide, a first conductive agent that covers the surface of each particle of the composite oxide, and a first conductive material interposed between the particles of the composite oxide and having a specific surface area of the first conductive material. A positive electrode active material including a second conductive agent smaller than the agent is described.
Japanese Patent Application Laid-Open No. 2000-123876 discloses that, while mixing a lithium-based composite oxide, a conductive agent and a binder, a pressing force and a shearing stress are applied to bind the conductive agent to the surface of the lithium-based composite oxide. A method for producing a positive electrode material which is subjected to a composite treatment by adhering with an agent is described.
[0005]
However, according to studies by the present inventors, lithium secondary batteries using these lithium-based composite oxides, particularly lithium-nickel-based composite oxides, have a high capacity but have low output in a low-temperature atmosphere. The problem of lowering has been found to be inherent.
In secondary batteries, cycle life is always considered important.
[0006]
[Problems to be solved by the invention]
The present invention provides a positive electrode active material composite particle that provides a lithium secondary battery having a high level of both output under a low-temperature atmosphere and cycle life, and a positive electrode and a lithium secondary battery using the composite particle. The task is to
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have performed a process of applying a compressive shear stress to a mixture comprising (A) a lithium-nickel-based composite oxide, (B) activated carbon, and (C) carbon black. It has been found that a lithium secondary battery produced using the positive electrode active material composite particles produced as described above has excellent output and cycle life in a low-temperature atmosphere, and has reached the present invention.
[0008]
That is, the gist of the present invention is characterized by being produced by subjecting a mixture comprising (A) a lithium / nickel-based composite oxide, (B) activated carbon and (C) carbon black to a treatment of applying compressive shear stress. In the lithium secondary battery positive electrode active material composite particles.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
The lithium-nickel composite oxide (A) constituting the positive electrode active material composite particles according to the present invention may further contain other elements in addition to lithium and nickel. The basic composition of this composite oxide is LiNiO₂, Li₂NiO₂, LiNi₂O₄And Li₂Ni₂O₄And those obtained by substituting a part of these nickels with other elements. Among them, those represented by the following general formula (I) are preferable.
[0010]
Embedded image
Li_aNi_bM_cO₂(I)
(Where a is a number from 0.9 to 1.2, b is a number from 0.5 to 1.2, b + c is a number from 0.9 to 1.2, and M is Be, B, Mg, Al , Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, and Ga.)
In the formula (I), when a exceeds 1.2 and b + c is less than 0.9, lithium replaces a large amount of nickel sites in the crystal, so that the battery capacity decreases. On the other hand, if a is less than 0.9 and b + c is 1.2 or more, the amount of lithium that can participate in charging and discharging of the battery decreases, so that the battery capacity decreases. Therefore, the upper limit of a is preferably 1.1 or less, particularly 1.05 or less, and the lower limit is preferably 0.95 or more. The lower limit of b + c is preferably 0.95 or more, and the upper limit is 1.1 or less, particularly preferably 1.05 or less. The lower limit of b is preferably at least 0.5, particularly preferably at least 0.55, and the upper limit is preferably at most 1.1, particularly preferably at most 1.05. Since M is not an essential component, c may be 0, and the upper limit is preferably 0.6 or less, particularly preferably 0.5 or less.
[0011]
M is preferably at least one element selected from the group consisting of B, Mg, Al, Ca, Cr, Mn, Fe and Co, and particularly from the group consisting of B, Al, Cr, Mn and Co. Selected ones are preferred. Of these, Al and / or Co are preferred, and Co is most preferred.
In the present invention, (A) a lithium-nickel-based composite oxide having an average primary particle diameter of 0.01 μm or more and 30 μm or less usually measured by SEM observation is used. The lower limit of the average primary particle size is preferably at least 0.02 μm, particularly preferably at least 0.1 μm, and the upper limit is preferably at most 5 μm, particularly preferably at most 2 μm.
[0012]
The average secondary particle diameter (average particle diameter) measured by a laser diffraction / scattering particle size distribution analyzer is usually 1 μm or more and 50 μm or less. The lower limit of the average secondary particle diameter is preferably 4 μm or more, and the upper limit is 40 μm or less, particularly preferably 30 μm or less.
Further, the specific surface area measured by the BET method (nitrogen surface area method) based on ASTM D3037 using a BET type powder specific surface area measuring device is usually 0.1 m²/ G or more 10.0m²/ G or less. The upper limit of the specific surface area is 5.0m²/ G or less, especially 2.0 m²/ G or less, and the lower limit is 0.5 m²/ G or more is preferred.
[0013]
(A) The lithium-nickel-based composite oxide can be prepared as a powder by mixing a lithium source compound, a nickel source compound, and other desired element source compounds and treating the mixture by a dry method or a wet method. .
Preferably, a slurry prepared by adding each of the above-mentioned element source compounds to a medium such as water and pulverizing and mixing with a wet pulverizer such as a medium stirring type pulverizer, or each element source compound pulverized by a dry pulverizer with water or the like After spray-drying the slurry prepared by mixing in the medium described above, followed by baking. Among them, it is preferable to use a wet method of pulverizing and mixing with a wet pulverizer.
[0014]
In the wet method, the solid content concentration in the slurry is usually from 10% by weight to 50% by weight. If it is less than 10% by weight, the particle size of the powder formed by the spray drying treatment does not fall within the preferred range. If it exceeds 50% by weight, a uniform slurry cannot be obtained. The solid concentration in the slurry is preferably 12.5% by weight or more and 35% by weight or less.
[0015]
The average particle diameter of the element source compound in the slurry is usually preferably 2 μm or less and 0.01 μm or more as a value measured by a laser diffraction / scattering particle size distribution analyzer. If it exceeds 2 μm, the reactivity at the time of firing will be low, and a material having a high bulk density cannot be obtained. It is not economical to grind to less than 0.01 μm. The upper limit of the average particle size is preferably 1 μm or less, particularly preferably 0.5 μm or less, and the lower limit is preferably 0.05 μm or more, particularly preferably 0.1 μm or more.
[0016]
The viscosity of the slurry is usually 50 mPa · sec or more and 3000 mPa · sec or less as a value measured by a BM type viscometer. If it is less than 50 mPa · s, the particle diameter of the powder formed by the spray drying treatment does not fall within the preferred range. If it exceeds 3000 mPa · s, the slurry becomes difficult to handle. The lower limit of the viscosity is preferably 100 mPa · sec or more, particularly preferably 200 mPa · sec or more, and the upper limit is preferably 2000 mPa · sec or less, particularly preferably 1600 mPa · sec or less.
[0017]
Examples of the lithium source compound or nickel source compound of the lithium-nickel composite oxide include oxides, hydroxides, carbonates, nitrates, sulfates, carboxylate salts such as acetates and oxalates, and alkylated compounds of the respective metals. And halides.
As the lithium source compound, Li₂O, LiOH, LiOH.H₂O, Li₂CO₃, LiNO₃, LiOCOCH₃, (LiOCO)₂, LiCH₃, LiC₂H₅, LiCl, LiI and lithium citrate. Of these, LiOH-H₂O, Li₂CO₃, LiNO₃Or LiOCOCH₃Especially LiOH ・ H₂O is preferred.
[0018]
NiO, Ni (OH) as the nickel source compound₂, NiOOH, NiCO₃・ 2Ni (OH)₂・ 4H₂O, Ni (NO₃)₂・ 6H₂O, NiSO₄, NiSO₄・ 6H₂O, NiC₂O₄・ 2H₂O, Ni (OCOCH₃)₂And NiCl₂And the like. Of these, NiO, Ni (OH)₂, NiOOH, NiCO₃・ 2Ni (OH)₂・ 4H₂O or NiC₂O₄・ 2H₂O, especially NiO, Ni (OH)₂Alternatively, NiOOH is preferred.
[0019]
(A) The raw material compounds of other elements that may be contained in the lithium-nickel composite oxide include oxides, hydroxides, carbonates, nitrates, sulfates, tungstates, and acetates of the respective metals. Carboxylates such as salts and oxalates, alkylated compounds, halides, and carbides are exemplified. Some of them are exemplified below.
MgO, Mg (OH) as a magnesium source compound₂, Mg (NO₃)₂・ 6H₂O, MgSO₄, MgC₂O₄・ 2H₂O, Mg (OCOCH₃)₂・ 4H₂O and MgCl₂And the like. Among them, MgO or Mg (OH)₂Especially Mg (OH)₂Is preferred.
[0020]
As the aluminum source compound, Al₂O₃, Al (OH)₃, AlOOH, Al (NO₃)₃・ 9H₂O, Al₂(SO₄)₃And AlCl₃And the like. Of these, Al₂O₃, Al (OH)₃Alternatively, AlOOH, particularly AlOOH, is preferred.
CaO, Ca (OH) as the calcium source compound₂, CaCO₃, Ca (NO₃)₂・ 4H₂O, CaSO₄・ 2H₂O, CaC₂O₄・ H₂O, Ca (OCOCH₃)₂・ H₂O and CaCl₂And the like. Of these, CaO, Ca (OH)₂Or CaCO₃Especially Ca (OH)₂Is preferred.
[0021]
As the chromium source compound, CrO, CrO₂, Cr₂O₃, Cr (OH)₂, Cr₂O₃・ NH₂O, CrSO₄・ 7H₂O, Cr₂(SO₄)₃, Cr (OCOCH₃)₂・ 2H₂O, Cr (OCOCH₃)₃, CrCl₂And CrCl₃And the like. Of these, CrO, CrO₂, Cr₂O₃, Cr (OH)₂Or Cr₂O₃・ NH₂O, especially CrO, CrO₂Or Cr₂O₃Is particularly preferred.
[0022]
As a manganese source compound, MnO₂, Mn₂O₃, Mn₃O₄, MnOOH, MnCO₃, Mn (NO₃)₂, MnSO₄, Mn (OCOCH₃)₂, Mn (OCOCH₃)₃, MnCl₂, MnCi₃And manganese citrate. Of these, MnO₂, Mn₂O₃, Mn₃O₄Or MnOOH, especially MnOOH₂, Mn₂O₃Or Mn₃O₄Is preferred.
[0023]
Fe source compounds include Fe₂O₃, Fe₃O₄, FeOOH, Fe (NO₃)₃・ 9H₂O, FeSO₄・ 7H₂O, Fe₂(SO₄)₃・ NH₂O, FeC₂O₄・ 2H₂O, FeCl₂And FeCl₃And the like. Of these, Fe₂O₃, Fe₃O₄Or FeOOH, especially Fe₂O₃, FeOOH are preferred.
As the cobalt source compound, CoO, Co₂O₃, Co₃O₄, Co (OH)₂, Co (NO₃)₂・ 6H₂O, Co (SO₄)₂・ 7H₂O, Co (OCOCH₃)₂・ 4H₂O and CoCl₂And the like. Of these, CoO, Co₂O₃, Co₃O₄Or Co (OH)₂Especially Co (OH)₂Is preferred.
[0024]
Spray drying of the slurry can be performed by any known method. A preferred method is to spray the slurry from the tip of the nozzle using a pressurized gas. Any nozzle can be used. For example, a nozzle having a triple tube structure that injects pressurized gas from the center and outer periphery and injects slurry in a ring shape from the inner periphery as described in Japanese Patent No. 2797080 is preferable. As the pressurized gas, air, nitrogen, or the like is preferable. The gas linear velocity is usually 100 m / sec or more and 1000 m / sec or less. It is preferably at least 200 m / sec, particularly preferably at least 300 m / sec. As the drying gas, it is preferable that heated air or nitrogen or the like having a temperature of usually 50 ° C. or more and 120 ° C. or less, preferably 70 ° C. or more and 100 ° C. or less be flowed downward from the upper portion to the lower portion. Particularly preferred is a method in which the slurry is jetted from the nozzle in the horizontal direction, and the drying gas is down-flowed so as to be perpendicular thereto.
[0025]
By spray drying, a spherical powder is obtained. The average particle diameter of the powder can be controlled by the spraying method, nozzle shape, pressurized gas injection speed, slurry supply speed, heated gas flow temperature, and the like. As a value measured by a laser diffraction / scattering type particle size distribution measuring device, usually, a powder having a particle size of 4 μm or more and 50 μm or less is obtained. It is preferable to obtain a powder having a particle size of 5 μm or more and 30 μm or less.
[0026]
This powder is fired in a box furnace, tubular furnace, tunnel furnace, rotary kiln, or other device by heating it under an oxygen-containing gas or oxygen gas atmosphere such as air or an inert gas atmosphere such as nitrogen or argon. To obtain a lithium-nickel-based composite oxide. The heating is preferably performed in an oxygen-containing gas or oxygen gas atmosphere.
The firing is usually performed at 700 ° C. or higher and 1050 ° C. or lower. If the temperature is lower than 700 ° C., the reactivity to the composite oxide is reduced. On the other hand, when the temperature exceeds 1050 ° C., defects occur in the layered structure of the composite oxide. The lower limit of the firing temperature is preferably 750 ° C or higher, particularly 800 ° C or higher, and the upper limit is preferably 1000 ° C or lower, particularly preferably 950 ° C or lower.
[0027]
The heating time is preferably 0.5 to 50 hours.
After the heat treatment, it is preferable to gradually cool at a rate of 5 ° C./min or less.
(B) Any activated carbon can be used. Usually, those having an average particle diameter of 1 μm or more and 30 μm or less are used. The specific surface area by the BET method is 500 m²/ G or more and 3000m²/ G or less is preferable. 500m²/ G, the effect of improving the output of the battery in a low-temperature atmosphere is reduced, while 3000 m²/ G, the bulk density of the positive electrode active material-containing layer decreases, and the capacity per volume decreases. The lower limit of the specific surface area is 600m²/ G or more, especially 800 m²/ G or more is preferred. Most preferred is 1000m²/ G or more. The upper limit is 2800m²/ G or less, especially 2600 m²/ G or less is preferred.
[0028]
(C) Any carbon black can be used as long as it has conductivity. They may be used alone or in combination of two or more.
The average particle diameter of the carbon black is usually from 1 nm to 500 nm as a primary particle diameter. If it is less than 1 nm, it is not preferable in terms of production. On the other hand, when it exceeds 500 nm, it becomes difficult to impart conductivity to the positive electrode active material-containing composition. The lower limit of the average particle diameter is preferably 5 nm or more, and the upper limit is preferably 100 nm or less.
[0029]
Specific examples of carbon black include commercially available acetylene black, special furnace black commercially available as “Ketjen Black” (manufactured by Ketjen Black International), and “Mitsubishi conductive carbon black” or “Mitsubishi carbon black”. "(Manufactured by Mitsubishi Chemical Corporation).
[0030]
The positive electrode active material composite particles according to the present invention are obtained by subjecting a mixture containing each of the components (A) to the lithium-nickel-based composite oxide, (B) to activated carbon and (C) to carbon black by applying a compressive shear stress. It is manufactured by performing.
As a composition of this mixture, (A): 75 to 99.8% by weight, (B): 0.1 to 15% by weight, and (C): 0.1 to 10% by weight. % Or less is preferable.
[0031]
The lower limit of (A) is preferably at least 82% by weight, particularly preferably at least 87% by weight. The upper limit is preferably 97% by weight or less, particularly preferably 95% by weight or less.
If (B) is less than 0.1% by weight, the characteristics at low temperatures are deteriorated. On the other hand, if it exceeds 15% by weight, the battery capacity per volume decreases. The lower limit is preferably 2% by weight or more, particularly preferably 3% by weight or more. The upper limit is preferably 12% by weight or less, particularly preferably 8% by weight or less.
[0032]
If (C) is less than 0.1% by weight, a sufficient output improving effect cannot be obtained. On the other hand, when the content exceeds 10% by weight, the resistance of the composite particles increases, which hinders the output at low temperatures. The lower limit is preferably 1% by weight or more, particularly preferably 2% by weight or more. The upper limit is preferably 6% by weight or less, particularly preferably 5% by weight or less.
In the carbon component obtained by combining (B) and (C), the content of (B) is preferably 25% by weight or more and 95% by weight or less. When (B) is less than 25% by weight, the effect of improving the low-temperature characteristics is reduced. On the other hand, when (B) exceeds 95% by weight, the high-temperature cycle life is reduced. The lower limit of (B) is preferably at least 40% by weight, particularly preferably at least 50% by weight, and the upper limit is preferably at most 90% by weight, particularly preferably at most 80% by weight.
[0033]
The process of applying a compressive shear stress is described in JP-A-11-154515 and JP-A-2000-123876, in which components (A), (B) and (C) are blended at a predetermined ratio. This means an operation of applying compressive and shear stress as in the case of the method. In this way, the compressed compound is integrated, and a part of the integrated material is shaved by shearing stress to become fine powder, which is bonded to the integrated particles again, so-called mechanofusion is exhibited. It is considered. This processing can be performed using, for example, "Mechano Fusion System" (manufactured by Hosokawa Micron), "Hybridization System" (manufactured by Nara Machinery Co., Ltd.), or the like.
[0034]
A lithium secondary battery positive electrode active material composite is obtained by adding (D) a conductive agent and (E) a binder to the lithium secondary battery positive electrode active material composite particles obtained by the above mechanofusion treatment and mixing them. A particle-containing composition is prepared.
(D) As the conductive material, any material known to be used for a lithium secondary battery can be used. Examples include carbon black and graphite.
[0035]
As the binder (E), any of those known to be used in lithium secondary batteries can be used. For example, resins such as polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate and polyethylene; rubbers such as styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, and fluoro rubber; polymer substances such as polyvinyl acetate and cellulose Is mentioned.
[0036]
As the composition containing the composite particles of the positive electrode active material for a lithium secondary battery, 70% by weight or more and 98.9% by weight or less of the composite particles, (D) 1% by weight or more and 10% by weight or less of the conductive material, and (E) Those containing 0.1% by weight or more and 20% by weight or less of the adhesive are preferred.
When the composite particles are less than 70% by weight, it is difficult to sufficiently secure battery characteristics such as battery capacity. On the other hand, if it exceeds 98.9% by weight, it is difficult to secure the mechanical strength as an electrode. The composite particles preferably contain at least 75% by weight, particularly at least 80% by weight, and the upper limit is at most 97% by weight, particularly preferably at most 95% by weight.
[0037]
(D) If the amount of the conductive agent is less than 1% by weight, it is difficult to obtain a good cycle life. On the other hand, if it exceeds 10% by weight, the volume battery capacity decreases. The lower limit of (D) is preferably at least 2% by weight, particularly preferably at least 3% by weight, and the upper limit is preferably at most 10% by weight, particularly preferably at most 5% by weight.
(E) When the amount of the binder is less than 0.1% by weight, it is difficult to secure the mechanical strength as an electrode. On the other hand, if it exceeds 20% by weight, battery characteristics such as battery capacity and conductivity cannot be sufficiently ensured. The lower limit of (E) is preferably at least 3% by weight, particularly preferably at least 5% by weight, and the upper limit is preferably at most 15% by weight, particularly preferably at most 10% by weight.
[0038]
It should be noted that LiFePO 4 was further added to the lithium secondary battery positive electrode active material composite particle-containing composition.₄And other positive electrode active materials capable of inserting and extracting lithium ions.
A coating solution prepared by dispersing the obtained lithium secondary battery positive electrode active material composite particle-containing composition in a solvent is applied to the surface of the current collector, dried, and then subjected to a consolidation treatment using a uniaxial press or a roll press. Is carried out to produce a positive electrode of a lithium secondary battery having a layer made of the composition containing the composite particles of a positive electrode active material for a lithium secondary battery on the surface of the current collector.
[0039]
Examples of the solvent include ether solvents such as ethylene oxide and tetrahydrofuran; ketone solvents such as methyl ethyl ketone and cyclohexanone; ester solvents such as methyl acetate and methyl acrylate; amine solvents such as diethyltriamine and N, N-dimethylaminopropylamine. Aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide and dimethylacetamide; and water.
[0040]
Examples of the material of the current collector of the positive electrode include aluminum, stainless steel, nickel-plated steel, and the like. Its thickness is usually 1 to 1000 μm. It is preferably from 5 to 500 μm, particularly preferably from 5 to 100 μm. As the current collector of the positive electrode, an aluminum foil is preferable.
The composition layer containing the lithium secondary battery positive electrode active material composite particles on the surface of the current collector is usually manufactured to have a thickness of 1 to 1000 μm. Those having a thickness of 10 to 200 μm are preferred.
[0041]
The production of the negative electrode may be performed according to a conventional method. For example, there is a method in which a coating solution prepared by dispersing a negative electrode active material in a solvent together with a binder is applied to the surface of the current collector, dried, and subjected to a consolidation treatment by a uniaxial press, a roll press, or the like.
As the negative electrode active material, lithium, lithium aluminum alloy; graphite, coal-based or petroleum-based coke carbide, coal-based or petroleum-based pitch carbide, needle coke, pitch coke, carbide such as phenolic resin or crystalline cellulose, furnace black or Carbon black such as acetylene black; SnO, SnO₂, Sn_1-xM¹ _xO (where M¹Represents Hg, P, B, Si, Ge or Sb, and x represents a number satisfying 0 <x <1. ), Sn₃O₂(OH)₂, Sn_3-xM² _xO₂(OH)₂(Where M²Represents Mg, P, B, Si, Ge, Sb or Mn, and x represents a number satisfying 0 <x <3. ), LiSiO₂, SiO₂Or LiSnO₂And the like.
[0042]
As the binder, any of those known to be used in lithium secondary batteries can be used. For example, resins such as polyvinylidene fluoride, polytetrafluoroethylene, polymethyl methacrylate and polyethylene; rubbers such as styrene butadiene rubber, acrylonitrile butadiene rubber, ethylene propylene rubber, and fluoro rubber; high molecular substances such as polyvinyl acetate and cellulose Is mentioned.
[0043]
Examples of the solvent include ether solvents such as ethylene oxide and tetrahydrofuran; ketone solvents such as methyl ethyl ketone and cyclohexanone; ester solvents such as methyl acetate and methyl acrylate; amine solvents such as diethyltriamine and N, N-dimethylaminopropylamine. Aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide and dimethylacetamide; and water.
[0044]
Examples of the material of the current collector of the negative electrode include foils of copper, nickel, stainless steel, nickel-plated steel, and the like, and among them, copper foil is preferable.
As the electrolyte, any of those known to be used for lithium secondary batteries can be used. For example, an electrolyte used for an organic electrolyte, a solid polymer electrolyte, a gel electrolyte, an inorganic solid electrolyte, and the like can be mentioned. Among them, the electrolyte used for the organic electrolyte is preferable.
[0045]
Examples of the electrolyte used for the organic electrolyte include LiCl, LiBr, and LiClO.₄, LiAsF₆, LiPF₆, LiBF₄, LiB (C₆H₅)₄, LiCH₃SO₃, LiCF₃SO₃, LiN (SO₂CF₃)₂, LiN (SO₂C₂F₅)₂, LiN (SO₃CF₃)₂And LiC (SO₂CF₃)₃And the like.
[0046]
Examples of the organic solvent include diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolan, and 4-methyl-1,3- Ethers such as dioxolane; ketones such as 4-methyl-2-pentanone; fatty acid esters such as methyl formate, methyl acetate, methyl propionate; dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate , Butylene carbonate, vinylene carbonate and other carbonates; lactones such as γ-butyrolactone and γ-valerolactone; halogenated hydrocarbons such as 1,2-dichloroethane; sulfolane such as sulfolane and methylsulfolane Nitriles such as acetonitrile, propionitrile, butyronitrile, valeronitrile and benzonitrile; amines such as diethylamine, ethylenediamine and triethanolamine; phosphates such as trimethyl phosphate and triethyl phosphate; Aprotic polar solvents such as N-dimethylformamide, N-methylpyrrolidone, and dimethylsulfoxide;
[0047]
Among these, a high dielectric constant solvent having a relative dielectric constant of 20 or more at 25 ° C. is preferable. As such a solvent, ethylene carbonate and propylene carbonate, and a compound in which a hydrogen atom thereof is substituted with a halogen atom, an alkyl group or the like are preferable. The proportion of the high dielectric constant solvent in the whole organic solvent is usually 20% by weight or more. It is preferably at least 30% by weight, particularly preferably at least 40% by weight.
[0048]
A separator may be interposed between the positive electrode and the negative electrode of the lithium secondary battery. As the separator, a polyolefin such as polyethylene and polypropylene; a microporous film of a polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyester, polyamide, polysulfone, polyacrylonitrile, cellulose and cellulose acetate; Non-woven fabric filters such as glass fiber are exemplified. Of these, polyethylene microporous films are preferred. Polyethylene having a molecular weight of 500,000 or more and 5,000,000 or less is preferable. If it is less than 500,000, it is difficult to maintain shape retention at high temperatures. On the other hand, when the amount exceeds 5,000,000, it becomes difficult to secure microporous obstruction at a high temperature. The lower limit of the molecular weight is preferably 1,000,000 or more, particularly preferably 1.5,000,000 or more, and the upper limit is preferably 4,000,000 or less, particularly preferably 3,000,000 or less.
[0049]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples as long as the gist is not exceeded.
In the following Examples and Comparative Examples, (A) lithium / nickel based composite oxide, (B) activated carbon, (C) carbon black, (D) conductive material, and (E) binder were as follows: Was used.
[0050]
The lithium secondary battery positive electrode active material composite particles were produced by applying a compressive shear stress for 20 minutes at a rotation speed of 2600 rpm using a mechanofusion system “AM-20FS” (manufactured by Hosokawa Micron Corporation).
(A) Lithium nickel composite oxide
A-1: average secondary particle diameter 9 μm, specific surface area 0.7 m by BET method²/ G Li_1.05Ni_0.80Co_0.15Al_0.05O₂Lithium-nickel-cobalt-aluminum composite oxide represented by
A-2: average secondary particle system 7 μm, specific surface area 0.5 m by BET method²/ G Li_1.05Ni_0.80Co_0.15Al_0.05O₂A layered lithium-nickel-cobalt-aluminum composite oxide represented by the formula:
[0051]
(B) Activated carbon
Average particle size 6μm, specific surface area 1000m by BET method²/ G of activated carbon.
(C) Carbon black
Average primary particle system 30nm, BET specific surface area 1280m²/ G Ketjen Black (Ketjen Black International).
[0052]
(D) Conductive material
D-1: average primary particle system 30 nm, specific surface area 800 m by BET method²/ G Ketjen Black (Ketjen Black International)
D-2: average primary particle diameter 35 nm, specific surface area 39 m by BET method²/ G of acetylene black (manufactured by Denki Kagaku Kogyo KK).
[0053]
(E) Binder
Polyvinylidene fluoride “PVDF # 1100” (manufactured by Kureha Chemical Industry).
Examples 1-3, Comparative Examples 1-4
Using the compositions shown in Table 1, (A), (B) and (C) were used to produce lithium secondary battery cathode active material composite particles.
[0054]
[Table 1]

[0055]
Further, using the composite particles (D) and (E) obtained above with the compositions shown in Table 2, a composition containing lithium secondary battery positive electrode active material composite particles was produced.
In Comparative Example 1, the lithium secondary battery positive electrode active material composite particles obtained by subjecting the mixture of (A) and (C) to a process of applying compressive shear stress include (B), (D), and ( The composition containing particles of the lithium secondary battery positive electrode active material composite prepared by adding E) was used.
[0056]
[Table 2]

[0057]
A slurry obtained by dispersing each lithium secondary battery positive electrode active material composite particle-containing composition in N-methyl-2-pyrrolidone was applied to one surface of a 20-μm-thick aluminum foil, dried, and then 12 mm in diameter ( (12φ) was punched out and pressed to obtain a positive electrode. The amount of active material in the positive electrode was about 13 mg.
The positive electrode coating film punched out to 9φ was used as a test electrode, and a coin cell was assembled using Li metal as a counter electrode.²A charge / discharge test was performed at an upper limit of 4.2 V and a lower limit of 3.2 V at a constant current of, and the initial charge capacity per unit weight of the positive electrode active material [Qs (mAh / g)] and the initial discharge capacity [Qd1 (mAh / g)] ] Was measured.
[0058]
Further, 92.5 parts by weight of graphite powder having an average particle size of 8 to 12 μm and 7.5 parts by weight of polyvinylidene fluoride “PVDF # 1300” (manufactured by Kureha Chemical Industry) were dispersed in N-methylpyrrolidone. The slurry was applied to one side of a copper foil having a thickness of 20 μm, dried, punched into a circular shape having a diameter of 12 mm, and pressed to obtain a negative electrode.
[0059]
This negative electrode was used as a test electrode, and a coin cell was assembled using lithium metal as a counter electrode.²The initial storage capacity [Qf (mAh / g)] per unit weight of the negative electrode active material was measured when the reaction for storing lithium ions in the negative electrode at a constant current of 0 V was performed at a lower limit of 0 V.
A positive electrode is placed on the positive electrode can, a 25 μm-thick porous polyethylene film is placed thereon as a separator, pressed with a polypropylene gasket, the negative electrode is placed thereon, and a spacer for thickness adjustment is further placed. Was placed. In addition, a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio of 3: 7) was mixed with lithium hexafluorophosphate (LiPF).₆) Was added so as to have a concentration of 1 mol / liter, and the resulting mixture was sufficiently immersed. Then, a negative electrode can was placed and sealed to prepare a coin cell. The weight of the positive electrode active material / the weight of the negative electrode active material = {[Qf (mAh / g)] / 1.2} / [Qc (mAh / g)].
[0060]
With respect to the coin cell, the conditioning current value [I (mA)] = [Qd1 (mAh / g)] × the weight of the positive electrode active material / 5, the charge upper limit voltage of 4.1 V and the discharge lower limit voltage of 3.0 V, and two cycles of charge / discharge. Initial conditioning was performed, and the discharge capacity [Qd2 (mAh / g)] per unit weight of the positive electrode active material in the second cycle was measured.
[0061]
After the battery was sufficiently relaxed, the battery was charged for 72 minutes at a constant current of 1 / (3C), where 1 hour rate current value [1C (mA)] = [Qd2 (mAh / g) × weight of positive electrode active material, Was placed. Next, after leaving still in a low temperature atmosphere of -30 ° C for 1 hour or more, discharging was performed at a constant current of 2.5C for 4 seconds. Chronopotentiometry was measured by measuring the difference (ΔV) between the OCV immediately before the discharge (Open Circuit Circuit Voltage) and the OCV 4 seconds after the discharge. The results are shown in Table 2. The smaller the ΔV, the smaller the resistance of the battery, the more power can be taken out, and the higher the output under a low-temperature atmosphere.
[0062]
Further, the coin cell after the initial conditioning was charged and discharged 100 cycles at a constant current of 1 C, a charge upper limit voltage of 4.1 V, and a discharge lower limit voltage of 3.0 V in a 60 ° C. atmosphere. Subsequently, the charge / discharge of 0.2 mA was repeated twice, and the capacity after the cycle was confirmed. Chronopotentiometry was measured using the second discharge capacity after the cycle as Qd2 after the cycle. The results are shown in Table 3.
[0063]
[Table 3]

[0064]
【The invention's effect】
By using the composition containing the lithium secondary battery positive electrode active material composite particles according to the present invention, a lithium secondary battery having excellent output and cycle life under a low-temperature atmosphere can be manufactured.

Claims (11)

A lithium secondary battery positive electrode active material composite produced by subjecting a mixture comprising (A) a lithium nickel-based composite oxide, (B) activated carbon and (C) carbon black to a process of applying compressive shear stress. Particles. The lithium secondary battery cathode active material composite particles according to claim 1, wherein the lithium-nickel composite oxide is a composite oxide represented by the following general formula (I).

(Where a is a number from 0.9 to 1.2, b is a number from 0.5 to 1.2, b + c is a number from 0.9 to 1.2, and M is Be, B, Mg, Al , Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, and Ga.) The lithium secondary battery positive electrode active material composite particles according to claim 2, wherein M is an element selected from the group consisting of B, Al, Cr, Mn, and Co. Activated carbon, a lithium secondary battery positive electrode active material composite particles according to any one of claims 1 to 3 BET specific surface area is characterized in that it is of less 500 meters ² / g or more 3000 m ² / g. (A) lithium / nickel-based composite oxide: 75 to 99.8% by weight, (B) activated carbon: 0.1 to 15% by weight, and (C) carbon black: 0.1% by weight The lithium secondary battery positive electrode active material composite particles according to any one of claims 1 to 4, comprising 10 wt% or more. The lithium according to any one of claims 1 to 5, wherein in the carbon component (B) including the activated carbon and (C) carbon black, the content of the activated carbon (B) is 25% by weight or more and 95% by weight or less. Secondary battery positive electrode active material composite particles. The method according to any one of claims 1 to 6, wherein (A) a lithium-nickel-based composite oxide, (B) activated carbon, and (C) carbon black are mixed and then subjected to a treatment for applying a compressive shear stress. A method for producing composite particles. A composition comprising lithium secondary battery positive electrode active material composite particles, comprising the lithium secondary battery positive electrode active material composite particles according to any one of claims 1 to 6, a conductive material, and a binder. Lithium secondary battery positive electrode active material composite particles: 70% to 98.9% by weight, conductive agent: 1% to 10% by weight, and binder: 0.1% to 20% by weight. The composition according to claim 8, wherein the composite material comprises particles of a positive electrode active material for a lithium secondary battery. A positive electrode comprising a layer comprising the lithium secondary battery positive electrode active material composite particle-containing composition according to claim 8 or 9 on the surface of the current collector. A lithium secondary battery comprising the positive electrode, the negative electrode, and an electrolyte according to claim 10.